The present invention relates to an expansion device for reducing the pressure of refrigerant flowing from the condenser to the evaporator in a sealed refrigeration system. Specifically, the present invention relates to an expansion device, commonly referred to as a flow restrictor, formed from a tubular restrictor having a nozzle portion wherein the restrictor is brazed in a predetermined position within a metallic tube connecting the condenser with the evaporator.
A sealed refrigeration system includes a compressor, a condenser, an expansion device and an evaporator connected in a circuit to provide refrigeration. Hot compressed refrigerant vapor from the compressor enters the condenser, where it transmits heat to an external heat exchange medium and condenses. Condensed refrigerant at a high pressure flows through the expansion device, where the refrigerant undergoes a pressure drop and at least partially flashes to a vapor. The liquid-vapor mixture flows through the evaporator and absorbs heat from the warm external surroundings to evaporate and usually superheat the refrigerant. The low pressure refrigerant vapor then returns to the compressor to complete the circuit.
Although the expansion device or flow restrictor is often of simple construction, its role in the refrigeration system is such that refrigerant leaving the evaporator is super heated in a controlled manner. The performance of the expansion device also plays a crucial role in the capacity of the system.
The simplest and most commonly used flow restrictor or expansion device is the capillary tube. In operation, refrigerant from the condenser enters the capillary and undergoes a fictional pressure drop along the length of the tube. The capillary tube is relatively inexpensive to manufacture and install but has several shortcomings.
The capillary tube is typically a thin-walled copper tube of small diameter wound in a loop-like form for an easier mounting in the refrigerator or like apparatus. In producing this conventional flow restrictor device, it is necessary to loop the tube at a large radius of curvature such that the cross-section of the tube is not distorted which would adversely affect the pressure reducing performance. Consequently, the capillary tube occupies a large space and is relatively fragile and must be handled with care to avoid distortion.
The capillary tube must be connected to the refrigerant line between the condenser and the evaporator. Typically, this requires braze joints at the inlet and outer of the capillary tube. These joints are potential points of refrigerant leakage and add to the cost of installing the capillary tube into the refrigeration system.
It would be an improvement in the art, therefore, to provide a restriction device which overcame the problems of the capillary tube while maintaining the capillary tube benefits, namely low cost and ease in manufacturing.